Materials are being developed that resist moisture permeation in the range of 10−4 to 10−7 g/m2/day. These materials are particularly useful for flexible electronics and thin film applications. Calibrating these materials using a known water vapor transmission rate (WVTR) standard, however, is not possible using conventional methods. The normal limit of detection for commercially-available instruments is typically a WVTR of about 5×10−4 g/m2/day, and custom instruments have lower limits of detection from about 10−4 to 10−7 g/m2/day. However, no standards currently exist that are capable of calibrating any instrument below a WVTR of approximately 10−3 g/m2/day at a suitable temperature and relative humidity.
Related art WVTR standards, as well as related art standards for other analytes, are made from free-standing films of polymers with known permeation properties. However, as discussed above, these standards cannot be used to measure a WVTR below approximately 10−3 g/m2/day. Further, barriers that utilize thin film inorganic layers cannot be used as standards. A barrier may limit the permeable surface area by masking with a metallic foil or by coating with an oxide coating. However, any oxide or inorganic thin film coating is limited by its defects, including pinholes, grain size, and cracks. Further, these layers are easily cracked or damaged. Barriers may easily be damaged by mishandling, resulting in a change of the WVTR.
Accordingly, it would be advantageous to provide a calibrated standard that is capable of measuring a WVTR below approximately 10−3 g/m2/day. Further, it would be advantageous to provide standards for other analytes, such as oxygen or helium, with suitable transmission rates based on the analyte and the application for the standard.